Polar Bears in Manitoba

The Impacts of Climate Change
on Polar Bears in Hudson Bay

Thanks to the efforts of Canadian Wildlife Service biologists,
the Western Hudson Bay population is one of the best-studied
populations of polar bears in the world. Some of the results of
those studies are troubling. A warming trend has been observed in
the Arctic that has resulted in a three-percent loss to the
extent of the pack ice every decade since 1970. Coupled with a
spring break-up that is now occurring roughly three weeks earlier
than historical records indicate, these changes have serious
implications for polar bears.

Hudson Bay’s bears live on the ice hunting seals through the
winter and into the summer. When the ice melts, they move ashore
and survive on stored fat until the following winter when they can
hunt seals on the ice once again. Most bears fast for about four
months, however, pregnant females remain on land to give birth and
fast for about eight months. Early ice break-up cuts short their time
to hunt and build up their body condition, and longer ice-free
periods extend the time that the bears fast on shore. Studies have
shown that for each early week that break-up occurs, the bears
come ashore ten kilograms lighter and thus in poorer condition.

Warmer weather for Hudson Bay can have other catastrophic
impacts on polar bears. Spring rains can collapse maternity dens
before mother and cub have departed and can impact the maternity
dens of ringed seals, the primary prey species for Manitoba's polar
bears. If the ringed seal population declines as a result, the
polar bear population would decline in turn.

Warmer weather can also lead to an increase in the number of
forest and brush fires in areas where polar bears dig maternity
dens in peat. Fires melt the permafrost and without roots and
other plant debris to hold the roofs together, dens often
collapse. It can take 70 years after a fire for enough trees and
shrubs to grow back to allow the denning sites to be used again.

It is possible, that if our society does nothing to reduce the
emission of greenhouse gases, that the resulting global warming
may some day produce ice conditions in Hudson Bay that could not
support a population of polar bears.